Shell and tube heat exchangers are commonly used in the petrochemical, refining and power industries as effective means of exchanging heat between two flowing streams. The shell and tube heat exchangers generally contain a multitude of tubes contained within a cylindrical shell. The cylindrical shells are generally provided with removable headers at either end through which a first flowing fluid enters and leaves. Near each end of the shell tube sheets are provided to support the tubes, provide a header space and separate the first flowing fluid from the central portion of the shell by forcing the first flowing fluid into the tubes and then out into the opposite header space. The second flowing fluid enters the shell between the tube sheets and flows across the tubes exchanging heat with the first flowing fluid and then out of the shell. Depending upon the length of the shell and tube exchanger, a number of baffles are provided along the length inside the shell to support the tubes. The tube sheets and baffles all have individual holes which are in reasonable alignment lengthwise in the shell to accomodate each tube. Several hundreds or thousands of tubes may be utilized depending upon the diameter of the cylindrical shell. Additionally such heat exchangers may be forty to fifty feet long with commensurately long tubes.
During use, depending upon service, single tubes may become plugged. Some of the tubes may become cracked causing leakage from the shell side to the tube side or vice versa depending upon the pressures in the shell side and tube side. Also, corrosion and other factors may cause individual tubes to lose their physical integrity making the exchanger dangerous. Especially when cracks occur, the leaking tube must be identified and taken out of service. One common method of taking a tube out of service is simply to plug either end of the leaking tube. However, such practice effectively reduces the surface area available for heat transfer between the flowing fluids. When a tube becomes plugged or fouled the same net reduction in surface area results.
It may thus become desirable to replace individual tubes within a tube "bundle". This may be done in two fashions: (1) by removing the headers and pulling the entire tube bundle out of the shell or (2) by removing the headers and pulling the individual tube. The second method would be preferable because heavy equipment such as hoists and cranes are needed for the first. The time involved in the first is also considerable. However, while pulling an individual tube is relatively easy, the alignment of the replacement tube with the holes in the tube sheets and baffles is difficult or impossible, especially with longer exchangers.
The inherent problem in replacing an individual tube is its alignment with its holes in the baffles which themselves may not be in perfect alignment. One method of aligning the replacement tube with its holes is to cut a "window" in the shell and visually align the replacement tube with the holes. However, this is not desirable since cutting the "window" destroys the physical integrity of a "coded" vessel which would require special welding to close the "window" and inspection and testing after the "window" has been closed.
In an attempt to facilitate insertion of the replacement tube one heat exchanger company, The Thomas C. Wilson Co., provides a "tube guide" which may be inserted into the end of the replacement tube to assist in aligning the tube with its holes. The Wilson tube guide has a rounded bullet shaped head which extends from the replacement tube which is supposed to guide the tube into the hole. In other words, it replaces the squared off end of the tube with a solid tapered end. However, due to the tubes sagging between the baffles and the possible misalignment of the holes, alignment is still not easy and in some cases still impossible.
The inventors herein have experimented with using a rod which is inserted the length of the tube to be replaced and left hanging in the baffles after the tube is removed. The replacement tube would be placed over the rod and the rod would guide the tube through the holes in the tube sheets and baffles. While the inventors do not known if such a method has ever been used by others, experimentation has disclosed serious drawbacks. The rod rests on the lower part of the hole and sags between baffles. The blunt end of a tube simply follows the rod to the lower part of the hole and butts against the baffle preventing passage through the hole.
Thus a solution to easily replacing tubes in a shell and tube exchanger was seen to be needed. The advantages of the solution are obvious to those skilled in the art. A simple inexpensive system to quickly replace tubes in a tube bundle would save time and effort and thus money in returning a heat exchanger to service. The present invention provides such an easy and simple expedient for replacing tubes in a heat exchanger with the tube bundle in place. Using the system, tool and method described hereinbelow a sixteen foot tube has been replaced in a matter of seconds.